1. Field of the Invention
The present invention relates to an improvement of a hybrid motive power vehicle having an electric motor and an internal combustion engine and in more particular, to an improvement for suppressing a torque fluctuation caused in a power train system and in drive wheels when the power source is switched from one to the other.
2. Description of the Related Art
A hybrid motive power vehicle having an electric motor and an internal combustion engine as the power sources is already known, in which one or both of the power sources are activated for driving drive wheels.
In this type of hybrid motive power vehicle, switching from the electric motor to the internal combustion engine is performed by cranking (forcibly rotating) the internal combustion engine via a clutch. In this motive power switching, a torque fluctuation is generated in a motive power train system, which makes the vehicle running awkward.
This torque fluctuation includes a abrupt torque decrease generated at the initial stage of the start of the internal combustion engine when the electric motor which has been used only for running of the vehicle is used as a starter of the internal combustion engine, and a abrupt torque increase generated at the final stage of the start of the internal combustion engine when the internal combustion engine which has been functioning as a load of the electric motor starts rotation by itself.
In order to solve these problems, Japanese Patent Publication 6-17727 has suggested a hybrid type vehicle in which the drive torque of the electric motor is temporarily increased at the instant of clutch connection between the electric motor and the internal combustion engine, so as to prevent generation of the torque lowering. However, this does not solve the problem of the abrupt torque increase generated when the internal combustion engine has started.
Moreover, Japanese Patent Publication 10-212983 has suggested a motive power output apparatus which controls the ignition timing or the inlet valve open/close timing and the non-work fuel consumption, so as to suppress torque generated at the start of the internal combustion engine, preventing the abrupt torque increase. However, in order to suppress and control the torque, the structure of the internal combustion engine has become complicated, which increases the production cost.
It is therefore an object of the present invention to provide a hybrid motive power vehicle capable of smooth switching the power source from an electric motor to an internal combustion engine, realizing a stable running, using a simple configuration with solving the problems described above.
The hybrid motive power vehicle according to the present invention comprises: an electric motor and an internal combustion engine as power sources, so that at least one of the power sources is operated and its drive force is transmitted to drive wheels via a power train system common to the electric motor and the internal combustion engine; a power source switching unit for switching the power source between the electric motor and the internal combustion engine; a buffer clutch capable of adjusting a connection force and arranged in the power train system; and a clutch controller for maintaining the connection force of the buffer clutch in a half-clutch state while the power source switching unit is operating and setting the buffer clutch to a complete connection state when the operation of the power source switching unit is complete.
The power source switching unit selects a power source to be operated and switches the power source from the electric motor to the internal combustion engine, for example. While this switching is being performed, the clutch control means maintains the buffer clutch arranged in the power train system, in a half-clutch state. Accordingly, even if a torque fluctuation is generated in the vicinity of an output portion of the power source during a power source switching, the torque fluctuation is absorbed by slide of the buffer clutch in the half-clutch state. That is, the torque fluctuation will not be transmitted over the position of the buffer clutch to the downstream of the power train system. Thus, drive force fluctuation of the drive wheels is significantly reduced and it is possible to maintain a stable running while the power source switching is being performed.
Furthermore, in order to reduce the torque fluctuation itself generated in the vicinity of the output portion of the power source during a power source switching, the vehicle further comprises: a transmission arranged at an upstream position from the buffer clutch in the power train system and having an input shaft connected to an output shaft of the electric motor; and a start-up clutch capable of adjusting a connection force, through which clutch an output shaft of the electric motor is connected to an output shaft of the internal combustion engine, wherein the power source switching unit includes: a start-up condition setting block for setting a start-up control parameter for controlling an output of the internal combustion engine at starting the internal combustion engine, a stationary operation control parameter required for performing a stationary operation by the internal combustion engine alone, and a start-up condition block for setting a target rpm of the internal combustion engine required for reaching a running speed immediately before starting the power source switching; an internal combustion engine start-up control block for setting, in the internal combustion engine, the start-up control parameter set by the start-up condition setting block so as to increase the drive torque of the electric motor and connect the start-up clutch in the half-clutch state, so that the internal combustion engine is cranked by the electric motor so as to start the internal combustion engine; and a stationary operation start control block for confirming that the internal combustion engine is started and the internal combustion engine has reached the target rpm, returning the drive torque of the electric motor to a previous value, setting the start-up clutch to a complete connection state, setting, for the internal combustion engine, the stationary operation control parameter which has been set by the start-up condition setting block, and gradually reducing the torque application by the electric motor so as to start a drive by the internal combustion engine.
With this configuration, firstly, the clutch control means sets the buffer clutch to the half-clutch state. Next, the internal combustion start control block sets the start-up control parameter for the internal combustion engine, increases the drive torque of the electric motor, sets the start-up clutch to the half-clutch state, and connects the electric motor to the internal combustion engine. This starts a cranking of the internal combustion engine by the electric motor to increase the load of the electric motor. However, the drive torque of the electric motor has been increased and it is possible to prevent relative lowering of the output torque due to increase of the load. Moreover, the start-up clutch for transmitting the drive force of the electric motor to the internal combustion engine is in the half-clutch state. Accordingly, even if a torque fluctuation is generated when the electric motor is connected to the internal combustion engine, the fluctuation is very gentle and the substantial output torque is almost identical to the state when no load of the internal combustion engine affects the electric motor, i.e., the state before starting the cranking of the internal combustion engine.
Next, the internal combustion is started by the aforementioned cranking and the internal combustion engine starts spontaneous rotation, increasing its rpm, which is confirmed by the stationary operation start control block. However, combustion of the internal combustion engine at this stage is controlled according to the start-up control parameter set by the start-up condition setting block and accordingly, the output from the combustion is suppressed to a very low value. That is, the output at this stage substantially owes to rotation of the electric motor and the output torque, in the same way as has been described above, is almost identical to the state prior to starting crank and the value during the cranking of the internal combustion engine.
Next, when the rpm of the internal combustion engine has reached the target rpm set by the start-up condition setting block, this is detected by the stationary operation start control block. The drive torque setting of the electric motor is returned to a previous state, i.e., the state prior to starting the buffer clutch connection and the start-up clutch is set to a complete connection state so as to completely connect the electric motor to the internal combustion engine. At this stage, the internal combustion engine has reached the target rpm value, i.e., the rpm required for the speed immediately before switching the power source and this value is identical to the current rpm of the electric motor. That is, there is no difference between the internal combustion engine and the electric motor and no torque fluctuation is generated if the startup clutch is connected completely.
After the internal combustion engine is completely connected to the electric motor via the start-up clutch, the stationary operation start control block sets, for the internal combustion engine, the stationary operation control parameter enabling the internal combustion engine to operate solely, i.e., a parameter allowing a substantial torque output by the internal combustion engine and gradually reduces the torque application by the electric motor while starting drive by the internal combustion engine, so that the total of the output from the electric motor and the output from the internal combustion engine is almost identical, i.e., matched with the output of the electric motor immediately before starting connection of the start-up clutch.
The start-up control parameter for suppressing the output of the internal combustion engine at starting the internal combustion engine and the stationary combustion control parameter allowing a stationary operation of the internal combustion engine alone may utilize the fuel injection and ignition cycle, the throttle open degree, and the like.
For example, when using the fuel injection and ignition cycle of the internal combustion engine as a parameter, the setting for continuous fuel injection and ignition (for increasing the output torque) is the stationary operation control parameter and the setting for carrying out the fuel injection and ignition intermittently (for decreasing the output torque) is the start-up control parameter. Moreover, when using the throttle open degree as a parameter, the setting for increasing the throttle open degree within an appropriate range (for increasing the output torque) is the stationary operation control parameter and the setting for decreasing the throttle open degree (for decreasing the output torque) is the start-up control parameter. According to the configuration of the internal combustion engine, it is possible to adjust the ignition timing, the inlet valve open-close timing, the air/fuel ratio, or the like so as to control the output of the internal combustion engine.